Charles H. Spurgeon on Psalms 104:9

Thou hast set a bound, etc. In these words the psalmist gives us three things clearly concerning the waters. First, that once (he means it not of the deluge, but of the chaos), the waters did cover the whole earth, till God by a word of command sent them into their proper channels, that the dry land might appear. Secondly, that the waters have a natural propensity to return back and cover the earth again. Thirdly, that the only reason why they do not return back and cover the whole earth is, because God hath "set a bound, that they cannot pass." They would be boundless and know no limits, did not God bound and limit them. Wisdom giveth us the like eulogium of the power of God in this, Pr 8:29 "He gave to the sea his decree, that the waters should not pass his commandment." What cannot he command, who sendeth his commandment to the sea and is obeyed? Some great princes, heated with rage and drunken with pride, have cast shackles into the sea, as threatening it with imprisonment and bondage if it would not be quiet; but the sea would not be bound by them; they have also awarded so many strokes to be given the sea as a punishment of its contumacy and rebellion against either their commands or their designs. How ridiculously ambitious have they been, who would needs pretend to such a dominion! Many princes have had great power at and upon the sea, but there was never any prince had any power over the sea; that's a flower belonging to no crown but the crown of heaven. Joseph Caryl.